The present invention is generally directed to an apparatus for conducting contact mechanics measurements in multiple dimensions. More particularly, the invention is directed to a system for coupling three orthogonal one-dimensional force and displacement measuring systems for conducting contact mechanics measurements on a surface, where forces on the surface in any two orthogonal directions resulting from the application of a force in the third direction are minimized.
Many industries utilize thin and hard coatings that are scratch or wear resistant to extend the lifetime of their products or devices. Such industries have historically depended heavily on instrumented indentation for mechanical characterization of these coatings. These industries include the rigid magnetic storage (computer hard disk) industry, the flexible magnetic storage (VCR/Tape) industry, the optical coatings industry, the automotive (paint and chrome) industry, and the orthopedic industry. In many of these industries, particularly those involved with magnetic storage and retrieval, the thickness of these coatings has continually decreased over the past decade as the demands for increased performance have forced storage densities to increase.
As coatings have become thinner, many of the typical contact mechanics techniques used in the past in attempts to characterize such coatings have become obsolete. For example, depth-sensing indentation systems provide little if any meaningful information concerning coating properties in the plane of the coating. Although atomic force microscope systems have been used in attempts to gather mechanical information on properties of thin surface coatings in the plane of the surface, these systems are lacking in their ability to provide meaningful information due at least in part to coupling, also referred to herein as cross-talk, between different axes of measurement.
What is needed, therefore, is a contact mechanics measurement system that minimizes cross-talk between orthogonal measurement axes, so that forces and displacements in directions both normal to the coating surface as well as in the plane of the surface may be measured quantitatively.
The foregoing and other needs are met by a multidimensional surface mechanics measurement system for applying forces to a surface or imposing displacements of a surface from multiple directions and for minimizing coupling between the forces or displacements so applied. The system includes at least a first elongate member, a second elongate member, a coupler for coupling the first elongate member to the second elongate member, and a probe which is connected to the coupler and which has a contact point for contacting the surface. The first elongate member extends in a first axial direction, which in a preferred embodiment, is substantially normal to the surface. The second elongate member extends in a second axial direction that is substantially orthogonal to the first axial direction. The coupler includes structures for attaching the first and second elongate members to the coupler such that the second elongate member is disposed substantially orthogonal to the first elongate member when attached to the coupler.
Preferred embodiments of the system include a third elongate member extending in a third axial direction that is substantially orthogonal to the first and second axial directions. The coupler of these preferred embodiments includes a structure for attaching the third elongate member to the coupler, such that the third elongate member is disposed substantially orthogonal to the first and second elongate members.
Preferably, the free length of the elongate members ranges from about 12.7 mm to about 25.4 mm, the diameter of the elongate members ranges from about 400 xcexcm to about 440 xcexcm, and the ratio of free length to diameter of the elongate members ranges from about 37 to about 45. Preferably, the ratio of axial stiffness to transverse stiffness for each of the elongate members ranges from about 3,000 to 30,000, and is most preferably about 10,000. The elongate members are preferably formed from a material having a Young""s modulus of approximately 10 GPa to 500 GPa, and a coefficient of thermal expansion of approximately 1.0xc3x9710xe2x88x927 m/xc2x0C. to 1.0xc3x9710xe2x88x925 m/xc2x0C. These relationships between axial and transverse properties, as well as the relative positioning of the elongate members, provides for minimization of cross-talk between the measurement axes while maintaining the structural rigidity necessary to perform contact mechanics measurements. Thus, the system provides for accurate and quantitative measurement of forces and displacements in directions both normal to a surface, as well as in the plane of the surface.
In some preferred embodiments of the system, the coupler includes a first rigid member aligned with the first axial direction, a second rigid member aligned with the second axial direction, and a third rigid member aligned with the third axial direction. The structure for attaching the first elongate member to the coupler includes a first shaft into which a first end of the first elongate member is inserted. The structure for attaching the second elongate member to the coupler includes a second shaft into which a first end of the second elongate member is inserted. The structure for attaching the third elongate member to the coupler includes a third shaft into which a first end of the third elongate member is inserted. In these preferred embodiments, the first ends of the first, second, and third elongate members have outside diameters of substantially equal to but no greater than the inside diameters of the first, second, and third shafts, respectively.